The present invention relates to valve guide inserts, and in particular to a valve guide insert shaped to facilitate installation into a valve guide bore.
Valve guides in internal combustion engines can become worn through extended use. This is especially true when the valve guide is machined in a cylinder head cast from iron or other nondurable material. Techniques have been developed for reaming a worn guide and inserting a thin-walled, tubular member formed from phosphor bronze or similar material into the resultant bore to refurbish the guide.
The first such technique is disclosed in U.S. Pat. No. 3,828,756, issued to James Kammeraad and assigned to the assignee of the present invention. The technique includes forming a slitted tubular insert from a flat sheet of phosphor bronze material and press-fitting the insert into a reamed valve guide bore. The tubular member is properly sized so that the slit is substantially closed when the insert is fitted within the valve guide bore. A tool is then forced down the insert to work the metal to further seal the slit and also to form the surface of the insert contacting the valve stem. In some inserts, spiral grooves are formed on the surface contacting the valve stem to provide a path for supplying lubricating oil to the surface of the reciprocating valve stem.
An improvement to this insert is disclosed in U.S. Pat. No. 4,768,479, also issued to James Kammeraad and assigned to the assignee of the present invention. This patent teaches preforming on the interior surface of the thin-walled insert a series of discontinuous spiral grooves. These grooves act as oil reservoirs, furnishing oil to lubricate the reciprocating valve stem. The discontinuous nature of them prevents any tendency of the oil to flow through the insert into the combustion chamber.
Use of these thin-walled, phosphor bronze valve guide liners or inserts has become very popular, commencing in the early-to-mid-1970s, since they provide improved durability, improved heat transfer during operation of the engine, and also since less material needs to be removed from the engine cylinder head during reboring of the worn valve guide. The use of thin-walled phosphor bronze inserts has become so successful, in fact, that they are now being installed in production engines at the factory to increase the reliability of the valve guides.
One problem associated with the use of these thin-walled valve guide inserts is the tendency to crush or deform during installation. This tendency occurs not only at the leading end of the insert which is initially being driven into the valve guide bore, but at the trailing end as well, since that is where the driving force is applied. The thinner the insert, the more apt the installer is to encounter this problem. The preformed discontinuous spiral on the interior of the insert which is the subject of the aforenoted U.S. Pat. No. 4,768,479 has aggravated this tendency, since the grooves which result from the removal or displacement of material weaken the sidewalls even further.
The traditional method of installation compensates for this tendency to crush or deform by first encapsulating the insert in an installation sleeve having a funnel-like opening through which the insert is initially forced to radially compress it. The insert then traverses into a section of the installation sleeve which has an inner diameter basically equal to that of the valve guide bore into which the insert is installed. The installation sleeve is then placed over and in alignment with the valve guide bore, and a punch-like tool used to force the insert from the sleeve into the valve guide bore. The punch-like tool has a leading mandrel or pilot having an outer diameter approximately equaling the inner diameter of the compressed insert. The driver section of the tool, which is integrally formed and axially aligned with the mandrel has a circumferential driving shoulder which flares from the mandrel at a right angle and has an outer diameter slightly less than the outer diameter of the compressed insert and the inner diameter of the valve guide bore. See FIG. 4 of U.S. Pat. No. 3,828,756. The mandrel and installation sleeve restrain the insert from collapsing under the force of the driving shoulder. This method of installation, while effective, is somewhat time-consuming and requires extreme care on the part of the operator to insure that the installation sleeve directly overlies the valve guide bore.
Another prior art method is to bevel or chamfer the valve guide bore opening, and thus provide a funnel-like surface to direct the thin-walled insert into the valve guide bore during installation. The chamfered bore has been used in conjunction with the installation sleeve of the type discussed in U.S. Pat. No. 3,828,756, the chamfer, in this case, primarily functioning to reduce the degree of care which otherwise must be taken to insure that the installation sleeve directly overlies the valve guide bore. See Hungary Patent Publication 53831, filed May 16, 1989. The chamfered bore has also been used in conjunction with an installation sleeve which compresses only the top or driven part of the insert, the lead end of the insert being radially compressed by the chamfer and/or by an operator as the lead end enters the valve guide bore. In either case, chamfering the bore opening involves an extra manufacturing step and a special reamer. Also, the chamfering operation reams away material at the end of the valve guide bore which ought to be retained, since it supports the valve stem at the end of the valve guide bore where the lateral forces on the valve stem are most pronounced. Compounding this problem is the fact that many chamfering operations are not well controlled, leading to excessive material being removed.